Idle task and idle hook in FreeRTOS - Mini Project: Build & Apply

Using Idle Task and Idle Hook in FreeRTOS

📖 Scenario: You are working on a small embedded system using FreeRTOS. You want to understand how the system behaves when no other tasks are running and how to run a simple function during idle time.

🎯 Goal: Learn to create an idle hook function that runs when the FreeRTOS idle task is running. You will set up the idle hook and verify it by toggling a variable.

📋 What You'll Learn

Create a FreeRTOS idle hook function named vApplicationIdleHook

Enable the idle hook in FreeRTOSConfig.h by defining configUSE_IDLE_HOOK as 1

Inside the idle hook, toggle a global variable idleToggle between 0 and 1

Create a simple FreeRTOS task that does nothing but delay to keep the scheduler running

Print the value of idleToggle periodically in the main task to observe changes

💡 Why This Matters

🌍 Real World

Embedded systems often need to perform background or low-priority work when the CPU is idle. The idle hook lets you run code during these idle times without creating extra tasks.

💼 Career

Understanding the idle task and idle hook is important for embedded developers working with FreeRTOS to optimize CPU usage and power consumption.

1

Create a global variable idleToggle initialized to 0

Create a global variable called idleToggle and set it to 0.

FreeRTOS

# Create a global variable called idleToggle and set it to 0
# Your code here

Need a hint?

Use volatile int idleToggle = 0; to create a global variable that can be changed in the idle hook.

2

Enable the idle hook by defining configUSE_IDLE_HOOK as 1

Add a line to your FreeRTOSConfig.h file to define configUSE_IDLE_HOOK as 1.

FreeRTOS

volatile int idleToggle = 0;
// Define configUSE_IDLE_HOOK as 1 in FreeRTOSConfig.h
# Your code here

Need a hint?

In FreeRTOSConfig.h, add #define configUSE_IDLE_HOOK 1 to enable the idle hook feature.

3

Write the idle hook function vApplicationIdleHook to toggle idleToggle

Write the function void vApplicationIdleHook(void) that toggles the global variable idleToggle between 0 and 1 each time it runs.

FreeRTOS

volatile int idleToggle = 0;
#define configUSE_IDLE_HOOK 1

// Write the idle hook function below
// Your code here

Need a hint?

The idle hook function must be named exactly vApplicationIdleHook and toggle idleToggle using idleToggle = 1 - idleToggle;.

4

Create a simple FreeRTOS task to print idleToggle every second

Create a FreeRTOS task function called vPrintIdleToggleTask that prints the value of idleToggle every 1000 milliseconds using vTaskDelay. Then start the scheduler.

FreeRTOS

volatile int idleToggle = 0;
#define configUSE_IDLE_HOOK 1

void vApplicationIdleHook(void) {
    idleToggle = 1 - idleToggle;
}

// Create a task to print idleToggle every second
// Your code here

Need a hint?

Create a task that prints idleToggle every second using printf and vTaskDelay. Start the scheduler with vTaskStartScheduler().